Why is Ultraseven such a big deal?

The most heavily promoted modern Ultra is his kid, he constantly gets referenced back to, and the guy from Hajime no Ippo even uses his theme song.

What about him makes him stand out so much from the other classic Ultras? I'm only really familiar with him from Leo, and he seemed pretty cool there, he didn't seem that different from any other ultra rugged hard ass Showa guy